Examples of electromagnetically operated adjusting devices for gas exchange valves of this type are shown in EP-A 0 197 357, DE-OS 35 13 105 and DE-OS 23 35 150.
These known examples disclose an anchor plate which is caused to oscillate back and forth between and engage the pole surface associated with a pair of opposed electromagnets. Each electromagnet has disposed therein a solenoid which, when energized, provides current flow through the electromagnet and attracts the anchor plate to its corresponding pole surface. The anchor plate includes an extension member adapted to transfer movement to a valve stem of a gas exchange valve such that the contact of the anchor plate with a pole surface of either electromagnet results in either a closed or open position of the gas exchange valve. A spring system comprising a first spring disposed above the anchor plate and located about the central axis of the actuator assembly and a second spring disposed below the anchor plate and also located about the central axis of the actuator assembly, is provided to assist the movement of the anchor plate towards the pole surface of the opposing electromagnet as the associated solenoid is de-energized. The neutral or dead point of this spring system is located at about the central position of the anchor plate between the two opposing electromagnets.
During operation, if the anchor plate is in contact with one of the two electromagnets, then the spring system moves the anchor plate away from the pole surface of the contacted electromagnet as the solenoid associated with that electromagnet is de-activated. This permits the spring system to oscillate the anchor plate out past the dead point to the opposite electromagnet. If the opposite electromagnet is then excited by current (i.e., its solenoid is energized), the anchor plate gets caught and engages the pole surface of the opposing electromagnet. The change of position of the anchor plate activates the gas exchange valve to switch from an open to a closed position, or vice-versa.
DE-A 35 13 105 and EP-A 0 197 357 also disclose valve systems wherein the anchor plate is stressed symmetrically at both ends. Symmetrical stressing is provided by a pair of springs or packs of springs such that when either electromagnet is energized, the dead point of the spring system sits in the middle between the opposed electromagnets, thus making possible a symmetrical opening or closing of the gas exchange valve. One side of the symmetrical spring system presses directly against a structured piece (stem) that forms a unitary part of the anchor plate or against the anchor plate itself, while the opposite spring system presses against the valve tappet which in turn presses against the anchor plate, moving it again into its middle position. Difficulties arise in such systems from the aging of the springs and general wear and tear, so that after a certain period of operation the position of the mid-point of the system is no longer assured.
Therefore there is a definite need in the art to provide an improved spring system in electromagnetically operated adjusting devices for use in gas exchange valves for internal combustion engines which do not fatigue or weaken or undergo changes over a long operating lifetime.